Phenotypic quality may determine the development and expression of sec
ondary sexual characters. We studied the relationship between molt and
several measures of phenotypic quality in the sexually size-dimorphic
barn swallow (Hirundo rustica) in its winter quarters in Namibia. Mal
es were in a more advanced stage of molt than females and juveniles, a
nd the speed of molt as determined from the residual of the regression
of the size of the gap in wings caused by missing and growing feather
s on wing molt score (residual wing raggedness) was also higher in mal
es than in females and juveniles. Male barn swallows with long and sym
metric tail feathers had a more advanced stage of molt and molted at a
higher speed than males with short and asymmetric tails. Long-tailed
females had a delayed molt, and females with asymmetric tails had less
advanced molt and lower rates of feather growth than females with sym
metric tails. Molt of secondaries in juveniles also appeared to be les
s advanced if they had long tails. Adult barn swallows molted their ta
il feathers in an irregular sequence with the longest, outermost tail
feather usually replaced before the second or the third outermost feat
hers. Good body condition was positively associated with a high molt s
core for some feather tracts and a rapid wing molt in adult females an
d tail molt in juveniles. Mallophaga were only weakly negatively assoc
iated with primary and secondary molt score in adult females and speed
of wing molt in adult males. In conclusion, phenotypic quality of adu
lt male barn swallows as reflected by the expression of their secondar
y sexual character during the previous molt reliably reflected stage a
nd speed of current molt.